This invention relates to a simple apparatus for removing foreign material from an inside surface of a duct, such as a cylindrical duct carrying wood dust laden air or other fluids having foreign material entrained therein. Such dust or foreign material builds up on the inside surface of the duct increasing fluid flow resistance and potentially creating a fire hazard where the accumulation is flammable.
In a typical application of the apparatus of this invention, ducts transmitting fluid flow must be periodically cleaned, which is a labor intensive time consuming procedure. For example, in the wood and pulp industry, a duct is located above or adjacent the work area which removes wood dust laden air. Similarly, ducts commonly remove kiln or coal dust, paint and dust particles, etc. Such particles must be removed from the inside surface or surfaces of the duct to maintain the efficiency of the system.
Where the particulate material carried by the duct is flammable, such as wood or coal dust or paint particles, it is desirable to create a break in the fouling layer to prevent flame from propagating along the duct through the fouling layer. That is, it is very desirable in such applications to remove flammable particles from areas on the inside surface of the duct to create a dust free area or fire break which prevents propagation of flame through the duct. Further, a flow, pressure or temperature sensor may be rendered inoperative or inaccurate by fouling which must be removed from the duct wall.
The duct cleaning apparatus of this invention effectively removes foreign material from an inside surface of the duct where the apparatus is located and creates dust free areas preventing propagation of flame through the duct. Further, the duct cleaning apparatus may be utilized to continuously clean the area where sensors located within the duct.
The apparatus for cleaning a duct of this invention comprises an elongated flexible element extending inside the duct having a first end supported in the duct spaced from the inside surface and a second opposed free end. The elongated flexible element has a length sufficient to engage the inside surface of the duct and preferably has a length equal to or greater than the diameter of the duct. Most preferably, the length of the elongated flexible element is at least twice the diameter of the duct. The elongated flexible element removes foreign material on the inside surface and cleans the inside surface of the duct as fluid flow is maintained through the duct. The duct cleaning apparatus of this invention will be more efficient where the fluid through the duct is turbulent, i.e., where the Reynolds number is greater than 2,000. Turbulent flow will cause the elongated flexible element to continuously engage or impact the inside surface of the duct, thereby removing foreign material.
Where the duct is metallic, the elongated flexible element is preferably nonmetallic to avoid sparking. However, the elongated flexible element may take various forms including a rope-like element. In the preferred embodiment, the elongated element is a strap preferably formed of a woven fabric, such as nylon webbing. As stated above, the length of the elongated flexible element will depend upon several factors including the diameter or maximum width of the duct, the velocity and viscosity of the fluid and the foreign material entrained in the fluid. An elongated flexible element having a width of 2xe2x80x3 to 5xe2x80x3 and a thickness of about 0.3xe2x80x3 to 0.1xe2x80x3 is suitable. In a vertical duct having a 32xe2x80x3 diameter, a strap of nylon webbing having a length of 6xe2x80x2 or greater is particularly suitable.
The first end of the elongated flexible element may be affixed inside the duct by any suitable means, including a bracket or support rod which extends, for example, through the duct. The rod may be secured to the duct by any suitable means within the duct. Alternatively, conventional brackets affixed to the duct wall may be utilized. Where a single elongated flexible element is utilized, the first end of the flexible element is preferably supported within the duct generally in the center or longitudinal axis of the duct. A plurality or gang of elongated flexible elements may also be utilized, particularly where the diameter of the duct exceeds 4xe2x80x2 or the duct is rectangular or polygonal. Although the duct cleaning apparatus of this invention is particularly suitable for cleaning an internal surface of a cylindrical duct, the duct cleaning apparatus of this invention may also be utilized for cleaning an internal surface of a rectangular or polygonal duct, wherein an elongated flexible element may be located adjacent to but spaced from each surface of the duct.
The duct cleaning apparatus of this invention thus provides continuous cleaning action as long as fluid flow is maintained through the duct. No external power source is required and the apparatus requires no electronic or mechanical controls. The duct cleaning apparatus of this invention is inexpensive to manufacture and install and is capable of operating in any duct orientation. The duct cleaning apparatus of this invention results in only a very minimal increase in fluid flow resistance, requires no labor and minimal maintenance. Other advantages and meritorious features of the duct cleaning apparatus of this invention will be more fully understood from the following description of the preferred embodiments, the claims and the appended drawings, a brief description of which follows.